1. Field of the Invention
The present invention relates to an image reading device having a reader part for reading an image on an original, and an image forming apparatus including the reading device.
2. Description of the Related Art
In general, a flat-bed scanner is used as an image reading device for an image forming apparatus. When the flat-bed scanner is used for scanning bound originals (hereinafter referred to as “a book-type original”), such as a book, a magazine, or a document, a spread central portion (hereinafter referred to as “the book center”) of the book-type original is apt to be bent upward and rise from an original platen glass. For this reason, a portion of an image read from a book-type original which corresponds to the book center is often deformed, curved, or darkened. In a worse case, it is impossible to read an image from a book-type original.
To solve the problem, there has been proposed a technique for eliminating deformation of a read image in the sub scanning direction (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. H10-150534). According to this technique, distances between a reader part and a surface of an original on an original platen glass are detected, a height distribution of a spread part of the original is calculated based on the detected distances, and then a reading pitch in the sub scanning direction is varied based on the calculated height distribution spread part during scanning of the original. Further, there has been disclosed a technique of accurately determining the size of an original by calculating a distance along the surface thereof in a spreading direction based on the height distribution of the spread part of the original.
There has been disclosed a still another technique of calculating heights of respective points on a book-type original from an original platen glass of a general-purpose flat-bed scanner, based on the shape of the contour line of an image read by the scanner, and then correcting the read image based on the calculated heights (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. 2000-244729).
In the technique for eliminating deformation of a read image in the sub scanning direction, it is necessary to change the reading pitch of a reader part in the sub scanning direction according to the height of an original surface at each scanned position. Further, since the reader part is configured to read the original from above, a predetermined space is necessitated between an original platen glass and the reader part. For this reason, an image reading device using this technique is required to have a different system or configuration from that of a flat-bed scanner, which inevitably makes the device complicated and increases the size of the device. Therefore, in the case where the image reading device employing the technique is used as an image reading device for a copying machine, manufacturing costs become higher than in the case where a flat-bed scanner is used. In addition, a new space is required for installation of the device.
On the other hand, the technique of correcting a read image based on heights of respective points on a book-type original from an original platen glass is used for a flat-bed scanner, and hence in order to read an original, it is required to set the original on the original platen glass such that a surface of the original to be read faces downward. However, to turn pages of the book-type original, it is necessary to once set the book on the original platen glass such that the opened pages face upward, turn to a desired page, and then set the book again on the original platen such that the opened pages face downward. In short, whenever pages are read, the whole book-type original has to be turned over, which considerably reduces productivity in reading the book-type original.
Further, when the height of the book center exceeds a predetermined value, the reading depth of the reader part becomes larger than a readable depth, and hence image portions close to the book center cannot be read. As a consequence, the image portions in respective areas close to the book center are read as blackened images.
Furthermore, since a spread surface of a book-type original corresponding to two pages is read as one page, it is necessary to perform control for dividing the one page into two so as to copy the book-type original in accordance with its page layout.